Repeaters are often used to extend the coverage area of a network and facilitate reception and transmission of signals in areas of inadequate network coverage. A simple repeater system is a type of bi-directional amplifier that includes a donor antenna, a coverage antenna (or sometimes referred to as a service antenna), and signal processing circuitry. In a typical arrangement, the donor antenna is a directional antenna pointing toward a signal source, and the coverage antenna is a rebroadcast antenna. The signal processing circuitry (which typically includes a signal amplifier) may be configured to provide gain (e.g., at least 10 dB of gain in most applications) to the received signal and prepare the signal for rebroadcasting. In addition to amplification, the signal processing circuitry may act on the physical signal itself to reshape, retime, filter, or perform any combination of these functions on the physical signal before the signal is rebroadcasted using the coverage antenna.
Repeaters may use the same frequency or different frequencies to receive and rebroadcast the signal. When a repeater uses the same frequency to receive and rebroadcast signals (sometimes called an “on-frequency” repeater), a high degree of isolation between the received and transmitted signals is important for stable operation of the repeater. In practice, isolation is generally achieved by physically separating the donor antenna from the coverage antenna. For example, isolation is generally proportional to the vertical and/or horizontal separation of the donor antenna and the coverage antenna. Increased isolation may also be achieved using various interference cancellation techniques (e.g., echo cancellation techniques) and proper selection and design of the antenna types for the donor and coverage antennas.
A high degree of isolation between the donor antenna signal and the coverage antenna signal is particularly difficult to achieve, however, when a highly compact form factor is desired. A highly compact form factor can be achieved by having the donor antenna and the coverage antenna positioned back-to-back in a single package or system. In such systems, a high degree of physical separation between the donor antenna and the coverage antenna is generally not practical or not possible.
Increased isolation between the donor antenna signal and the coverage antenna signal typically results in less signal interference between the two antennas, higher signal integrity, and improved signal strength, which may, in turn, result in increased battery life of a mobile device, decreased emitted radiation from the mobile device, and an overall improved user experience.